Chemistry Reference
In-Depth Information
containing casein (e.g., sodium caseinate) or those containing whey proteins
(e.g., dried or condensed whey, whey protein concentrate, whey protein
isolate) (Marshall et al., 2003). Dried whey has been investigated as an
ingredient for ice cream for many years, principally due to reduced cost
(Leighton, 1944; Neilsen, 1963; Parsons et al., 1985). However, it is high in
lactose (
75-80%), which is a major limitation. It has now become quite
common to supplement the traditional sources of MSNF (condensed skim
milk or skim milk powder) with blended MSNF products that contribute
excellent functionality from the protein (emulsification, foaming and water
holding), while at the same time reducing total protein content in the dry
blended ingredient from 36%, as found in skim milk powder, to 20-25%, to
maintain mix costs lower than they would be if skim milk powder was used.
Ingredients in the blends include milk or whey protein concentrates or iso-
lates, perhaps modified chemically or via fermentation, perhaps also some
caseinates, and whey powder or lactose, for standardization. Much experi-
ence has been gained at blending these ingredients (Goff, 2003; Marshall
et al., 2003) and the quality of ice cream resulting from their use can be very
good. However, since most legal jurisdictions require a minimum total solids
level in ice cream mix formulations, care must be taken to ensure that the
lactose content in the formulation is not too high when formulating with
these high-lactose ingredients, due to issues of freezing point depression and
lactose crystallization.
III.3.
Contribution of Lactose to Freezing Point Depression
Freezing point depression is a colligative property, governed by Raoult's law
and influenced by the collective number of moles of solute in solution. Thus,
freezing point depression is a function of both the concentration of all the
solutes and their molecular weight. Consequently, in an ice cream mix, the
major contributors to freezing point depression are the sugars and milk salts
(Leighton, 1927; Smith and Bradley, 1983; Smith et al., 1984; Baer and
Keating, 1987; Jaskulka et al., 1993, 1995). Lactose is a disaccharide, mole-
cular weight 342 Da, and is present at a significant concentration (
6%), thus
it contributes approximately 30% (although this varies with formulation) of
the total freezing point depression of a mix (Marshall et al., 2003). As the mix
is frozen, solvent is removed with the conversion of water to ice, so that the
effective concentration of solutes in the unfrozen phase continues to rise with
decreasing temperature, leading to the process of freeze-concentration and
establishing the equilibrium ratio of ice to water as a function of temperature
(see Figure III.2). This is plotted as a freezing curve (Figure III.3), which is
unique to each formulation (Bradley and Smith, 1983; Bradley, 1984; De
